Flower: Corolla zygomorphic, yellow, red-patterned, 10–16 mm (0.4–0.65 in.) long. Petals 5; the upstanding the ‘standard’, the lateral two the ‘wings’, the lower two united to form the ‘keel’, overall shape of corolla being butterfly-like. Calyx 5-lobed. Stamens 10, separate. A single carpel. Inflorescence an axillary, long-stalked, 2–6-flowered umbel.

Of the genus Lotus plants that grow in Finland, bird’s-foot trefoil has spread the furthest north. The secret of its success is probably partly due to its different forms, which have adapted to grow in different habitats. This diverse species can be split into several variations which began to develop in their own ways at the end of the Ice Age. In a relatively short space of time they developed small differences with respect to their hairiness, the fleshiness of their leaflets, and the form and size of their flowers.

Shore-side meadows in south-western Finland and the Åland islands are home to var. alandicus and var. carnosus, while var. maritimus grows along the eastern and northern shores of the Gulf of Finland. Light-filled hillside forests in southern Finland have their own species var. arenosus, while var. corniculatus has arrived in south-western Finland in ancient times with people and settled in to coastal and inland areas there. Other variations grow as established aliens, such as var. sativus, which has secured a foothold in a number of places.

Narrow-leaf Bird’s-foot Trefoil

Lotus tenuis

Other plants in the genus grow mainly in busy harbours and around warehouses. Narrow-leaf bird’s-foot trefoil looks a lot like bird’s-foot trefoil. The clearest difference between the plants is that the former has lanceolate leaflets which have tapered tips. Greater bird’s-foot trefoil (also known as marsh bird’s-foot trefoil, L. pedunculatus) has a hollow stem, is abundantly flowered, and its calyx lobes arch outwards in the bud.